Effect of chemotherapy, vaccines and immunostimulants on innate immunity of goldfish infected with Aeromonas hydrophila

Abstract

We report the effect of various chemicals, vaccines and immunostimulants on innate immune mechanisms such as phagocytosis activity, superoxide anion production of blood leukocytes, complement activity and plasma lysozyme activity and disease resistance in goldfish Carassius auratus (23 +/- 2 g) against Aeromonas hydrophila on Days 15 and 30 post-infection. In infected fish, the administration of diets supplemented with either probiotics, tri-herbal extract or azadirachtin for 30 d significantly enhanced phagocytic activity; administration for 15 d had no effect. In fish treated with heat-killed and formalin-killed vaccines, and probiotics-, tri-herbal- and azadirachtin-supplemented diets, superoxide anion production was enhanced on Day 30. However, there was no superoxide anion production in fish treated with tetracycline, furanace, formalin or hydrogen peroxide. Complement activity was also significantly enhanced on Days 15 and 30 in fish groups treated with vaccine and probiotics-, tri-herbal- and azadirachtin-supplemented diets. Other groups had no complement activity. Lysozyme activity was significantly enhanced after 30 d in fish treated with heat-killed vaccine and probiotics-, tri-herbal- and azadirachtin-supplemented diets. The probiotics- and tri-herbal-containing diet administration groups had no mortality (0%) preceding the challenge with live A. hydrophila. Groups treated with heat- or formalin-killed vaccines or azadirachtin-supplemented diet suffered mortalities of 30, 35 and 10%, respectively, which represents an improvement of survival rate compared to untreated infected control groups. We conclude that probiotics-, tri-herbal- and azadirachtin-supplemented diets act as immunostimulants enhancing the goldfish innate immune response and disease resistance against A. hydrophila.